- Replace "crypto/rand" to "math/rand" for files content generation
- Remove swarm/network_test.go.Shuffle and swarm/btm/btm_test.go.Shuffle - because go1.9 support dropped (see https://github.com/ethereum/go-ethereum/pull/17807 and comments to swarm/network_test.go.Shuffle)
* swarm/storage/encryption: async segmentwise encryption/decryption
* swarm/storage: adapt hasherstore to encryption API change
* swarm/api: adapt RefEncryption for AC to new Encryption API
* swarm/storage/encryption: address review comments